1. Field of the Invention
The present invention relates to an electrical test instrument, and in particular to an electrical run test instrument of the type used to test an electrical product or device by running the product or device at its normal operating voltages and currents.
The run test instrument of the invention includes a switching matrix that enables the run test instrument to be interconnected with at least one external safety compliance test instrument so as to enable testing of the product at other than operating voltages and currents without having to disconnect the product from its initial connection to the run test instrument, and that further includes line leakage test capabilities. Safety compliance test instruments to which the run test instrument of the invention may be connected include instruments capable of performing dielectric withstand, insulation resistance, and ground bond tests, as well as multiple function test instruments capable of performing multiple different types of safety compliance tests.
2. Description of Related Art
The present invention is a run test instrument designed to be interconnected with a safety compliance instrument in order to simplify design of test sequences that include not only run tests but also safety compliance tests such as dielectric withstand, insulation resistance, and ground bond tests using a single test setup.
Run tests and safety compliance tests have traditionally been treated as completely separate types of tests. Safety compliance testing involves testing the performance of a product to determine risk of injury to persons or property by subjecting the product to stress resulting from high voltages or currents, while run testing involves testing the performance of the product at ordinary operating or line voltages and currents. Despite the differences, however, both run testing and safety compliance testing are now considered integral parts of design and manufacturing processes for a wide variety of electrical products, and a convenient way of integrating the two types of tests would, in many situations, significantly improve the efficiency of those processes.
One of the reasons that run testing and safety compliance testing have traditionally not been combined is that there are simply too many different types of safety compliance tests to combine them all into a single test instrument. Even though integration of different test instruments offers the advantage of convenience and, to an extent, cost savings, integration has the disadvantage that not all of the different types of safety compliance tests need to be performed on every product, and therefore manufacturers and testing agencies have tended to forego complete integration in favor of being able to purchase only those test instruments required for their particular product.
By way of background, descriptions of various types of safety compliance tests may be found in U.S. Pat. Nos. 6,011,398 and 6,054,865, which respectively disclose a line leakage tester and a multiple function dielectric withstand tester capable of performing insulation resistance and ground bond tests in addition to various types of dielectric withstand tests. The detailed descriptions in these patents illustrate the diversity of safety compliance tests that currently must be performed in various situations. For example, line leakage safety compliance testing is primarily used during development of a product to verify whether a design is safe by simulating possible problems which could occur if the product is faulted or misused while the product is operating under high line conditions (110% of the highest input voltage rating of the product), and measuring the amount of current to which a user of an electrical device is exposed. On the other hand, insulation resistance tests are used during design of a product to measure circuit-to-ground impedance by measuring leakage current when a non-destructive voltage (in general, lower than 1000 volts) is applied between the circuit and ground, while dielectric withstand or xe2x80x9chipotxe2x80x9d safety compliance tests may be required either during design or manufacturing to measure insulation integrity by subjecting a device to voltages substantially greater than those applied during normal operation (in general, twice the normal operating voltage, plus 1000 volts), and measuring all stray current. Finally, ground bond tests are used during design or manufacturing to measure the response of the ground circuit to potential fault currents that might result from defective insulation.
Run testing, in contrast, is carried out after final safety testing so that manufacturers can verify the functionality of their products, and to gather basic test data on the products. A run test system ideally allows the product to be powered up immediately after the safety tests are completed in order to measure Amperage, Voltage, Watts, and Power Factor by replacing conventional electrical test instruments such as voltmeters and ammeters with a single instrument that provides a more convenient connection to the product being tested, and an integrated control interface.
The present invention seeks to provide a more integrated test system that permits both run tests and safety compliance tests to be performed through a single test set-up, while still offering the advantage of modularity or separability so that the run test and safety compliance instruments can be purchased and used separately or together as situations warrant. The approach taken by the present invention is to integrate a line leakage test capability, and to offer other safety compliance test capabilities through an interface capable of accepting voltages and currents from various safety compliance instruments and supplying them through the run test connection to the product being tested, thereby maintaining the discrete nature of the run and safety compliance test instruments.
In a sense, the use of an appropriate interface to permit integrations of test capabilities while still providing separate instruments is a departure from the historical trend toward greater integration of test capabilities in a single instrument. For example, specific examples of prior test instruments that include both run testing and high voltage safety compliance testing features have in fact been disclosed in U.S. Pat. Nos. 3,368,146, 4,922,172, 5,568,058, and 5,652,526. Instead of providing a switching interface that connects separate instruments, however, each of the devices disclosed in these patents is an integral unit, with no provision for interconnectability.
The present invention, in contrast, does not attempt to completely integrate run test and safety compliance test instruments, but rather builds upon previous attempts to provide safety compliance testers with varying degrees of interconnectability, ranging from completely modular rack based systems, such as the ones disclosed in U.S. Pat. Nos. 4,402,055, 4,760,330, 4,763,124, 4,807,161, and 5,036,479 which utilize a common bus, central controller, and plug-in units, to fully automated integrated test instruments with GPIB interfaces for integrated or common control of line leakage and dielectric withstand tests. What distinguishes the invention from the modular systems disclosed in the inclusion of interconnection capabilities in a run test instrument, rather than just in a safety compliance test instrument, and in the specific manner in which the interconnectability is accomplished, through the use of a high voltage switching matrix rather than a purely modular, bus or backplane interconnected system.
By providing for interconnection of a run tester with safety compliance test instruments, so that the run testing set up can also be used for connecting the device under test to the safety compliance tester in order to simplify production testing, and to enable safety compliance tests to easily be added to a run testing routine, the invention facilitates implementation of a product testing system such as the one described in U.S. Pat. No. 6,038,521. In the system described in this patent, both run testing and safety compliance testing is used to provide a xe2x80x9cquality test system for electrical appliances,xe2x80x9d but the quality test system uses separate run testing and safety compliance test equipment, with no interconnectability between the separate test instruments. By enabling more convenient implementation of run tests and safety compliance tests, the invention offers significant improvements in design and manufacturing efficiency to the user of a system such as the one described in U.S. Pat. No. 6,038,521, which should ultimately result in improved product safety for all consumers.
It is a first objective of the invention to provide a product testing system that allows both run tests and safety compliance tests to be performed using a single connection to the product being tested, while still offering the advantage of separability or modularity.
It is a second objective of the invention to provide a run test instrument capable of being interconnected to various electrical safety compliance testers in order to provide a product testing system that allows tests to be performed by applying higher than normal voltages and currents to a product, and then running the product on line power, while using a single connection to the product.
It is a third objective of the invention to provide a run test instrument that:
is capable of measuring input voltage, amperage, power, and power factor of a product running on line current,
is capable of accurately measuring leakage current from the enclosure of the product being tested to the neutral of the input power,
includes improved display, set up, and calibration features, and
can be used as part of an integrated run test instrument that can interconnect to an electrical safety compliance tester.
These objectives are achieved, in accordance with the principles of a preferred embodiment of the invention, by providing an electrical test instrument having a connection to a product being tested or xe2x80x9cdevice under testxe2x80x9d (DUT), and that further includes a high voltage switching matrix and a high voltage input that enables connection of the test instrument to an external high voltage safety compliance device through the above-mentioned connection to the device under test.
Preferably, the inputs to the high voltage switching matrix of the preferred test instrument include at least a line voltage input, a line neutral input, a high voltage input, a ground bond/continuity input, and a high voltage/ground bond return, while the outputs from the high voltage switching matrix include a DUT line output, a DUT neutral output, an earth ground connection, and a connection to the DUT case or chassis, as well as taps for measuring input voltage, output voltage, and output current and for supplying the measurement results to analog-to-digital and comparison circuitry on a main control board for display or further processing. Switching between the various inputs and outputs is accomplished through the use of relays controlled by a processor on the main control board.
In addition to including a high voltage switching matrix that makes possible interconnection to an external safety compliance test instrument, the run test instrument of the preferred embodiment is capable of measuring input voltage, amperage, power, and power factor of a product running on line current, and also of accurately measuring leakage current from the enclosure of the product being tested to the neutral of the input power.
Additional features of the run test instrument of the preferred embodiment of the invention, which are shared by the safety compliance test instrument disclosed in U.S. Pat. No. 6,054,865, herein incorporated by reference, are an operator interface arranged to permit test parameters to be pre-programmed or set through a keypad accessible to a user of the instrument and a menu driven display screen, and a remote interface that permits pre-programmed test functions to be initiated through a remote input port, and pass/fail indicator functions to be reviewed via a remote output port in order to enable manual control of the instrument from a remote location.